The subject invention pertains to the art of numeric displays, and in particular to light emitting diode (LED) display elements and a circuit assembly for operating and testing operability of the elements themselves.
The invention is particularly applicable to a time of day (TOD) or timing display used in a home cooking range. Such display assemblies often comprise a numeric display of segmented LEDs, arranged to form four digits. The displays have been successfully utilized in the higher temperature environments required for range use. Such LEDs have the advantages of high reliability at low cost, while providing a display that has been readily accepted by users to conveniently convey the desired time and timing information. Setting of the time displayed by the LEDs is accomplished by an operator accessible switch assembly.
In accordance with conventional manufacturing and assembly standards, before any such display can be assembled into a heating range, the display itself, its control circuitry and the operating switches must be tested for operability. As far as the display elements themselves are concerned, such testing is mainly concerned with identifying circuit integrity such as microconnections although element operability is also tested. Tests for open or shorted circuits to the LED segment elements are performed. If each digit in the display is comprised of seven linear segments and a decimal point, then for each digit, eight separate segment elements exist and each must be tested for operability.
The most notable problem with preexisting testing routines for range display assemblies has been the requirement that a human operator must visually observe whether each and every display element is properly illuminated as they are powered. Any noticed failure in illumination indicates either a connection fault or a faulty LED element itself. Requiring an operator to actually look at the display to evaluate operability is a tedious and expensive task and has been found to be unacceptably ineffective in identifying the particular problems with the display elements, the microconnections or the operating switches. The tedium is easily appreciated by merely considering the circumstances of having to repeatedly view test illuminations of LED displays. Expense becomes a factor due to the cost of test equipment necessary to be operated by the human operator as well as the cost of operator time in performing the tests. The inefficiency of the test operation itself results from possible human error occurring due to the difficulty and stress of running the test over a long period of time, as well as ineffectiveness in identifying the actual nature of the fault or failure involved between wiring, LED or switch.
The present invention contemplates a new and improved LED control circuit and self test routine which overcomes the above-referred to problems and others to provide a new LED display assembly, which is simple in design, economical to manufacture and test, can readily withstand the heated environment of a cooking range and which provides a highly efficient means for executing a test routine obviating operator participation in the test itself.